Bags for packaging are previously known as shown by the front view of FIG. 11(A) and the opened-out view of FIG. 11(B). In order to facilitate the task of unsealing, such a bag 1000 for packaging is provided with lines of weakness in the form of perforations or modified perforations on a pair of opposite faces of bag 1000 (hereinbelow, the line of weakness provided of one of these mutually opposite faces 1000A will be called “line of weakness 2000” and the line of weakness provided on the other face 1000B will be termed “line of weakness 3000”). With the conventional bag for packaging 1000, the unsealing task can easily be performed by tearing using the region of line of weakness 2000 and line of weakness 3000 that are respectively provided in first face 1000A and second face 1000B. For example, Japanese Utility Model Number 2566444 discloses a bag for packaging provided with lines of weakness in the form of modified perforations.